The present invention relates generally to soap bars exhibiting antibacterial effectiveness and methods of producing the same, and more particularly to soap bars including soap components exhibiting antibacterial properties.
Antibacterial personal care compositions are known in the art. Especially useful are antibacterial cleansing compositions, such as soap bars, that typically are used to cleanse the skin and to destroy bacteria and other microorganisms present on the skin, especially the hands, arms, and face of the user. Antibacterial compositions are used, for example, in the health care industry, food service industry, meat processing industry, and in the private sector by individual consumers. The widespread use of antibacterial compositions indicates the importance that consumers place on controlling bacteria and other microorganism populations on skin.
Commercial soap bars conventionally comprise one or more xe2x80x9csoapsxe2x80x9d, which, for purposes of describing this component of the soap bars of the present invention, has the meaning as normally understood in the art: monovalent salts of monocarboxylic fatty acids. The counterions of the salts generally include sodium, potassium, ammonium and alkanolammonium ions, but may include other suitable ions known in the art. The soap bars also may include optional adjuvant ingredients such as moisturizers, humectants, water, fillers, polymers, dyes, fragrances and the like to effect cleansing and/or conditioning for the skin of the user.
Typically, the soap components in conventional soap bars comprise salts of long chain fatty acids having chain lengths of the alkyl group of the fatty acid from about 12 carbon atoms to about 18 carbon atoms in length. The particular length of the alkyl chain(s) of the soaps is selected for various reasons, including cleansing capability, lather capability, costs, and the like. It is known that soaps of shorter chain lengths are more water-soluble (i.e., less hydrophobic) and produce more lather compared to longer chain length soaps. Longer chain length soaps are often selected for cost reasons and to provide structure to the soap bars.
To provide an antibacterial property to such conventional soap bars, it is generally necessary to add germicides or antibacterial agents to the soap bars. Thus, for example, bars containing antimicrobials such as triclosan (i.e., 2,4,4xe2x80x2-trichloro-2xe2x80x2-hydroxy-diphenylether) and triclocarbanilide are known. However, the addition of antibacterial agents to soap bars to achieve antibacterial effectiveness can add cost to the soap bars due to the cost of the antibacterial agents themselves and the added costs of production of the soap bars.
Accordingly, there is a need for soap bars that exhibit enhanced antibacterial properties that are separate and distinct from those properties of added antibacterial agents. The present invention addresses this long-felt but unresolved need.
While the way in which the present invention addresses these needs is addressed in greater detail below, in general, the soap bars in accordance with various aspects of the present invention exhibit antibacterial effectiveness due to the antibacterial properties of the soap components comprising the bars, separate and distinct from any added antibacterial active agents. Such soap bars have surprising antibacterial effectiveness at relatively short contact times compared to conventional soap bars that typically comprise soap compositions of salts having 12 to 18 carbon atoms.
In accordance with an exemplary embodiment of the present invention, a soap bar that exhibits antibacterial effectiveness is provided. The soap bar comprises, by weight at least about 50% soap having alkyl chain lengths of 8-10 carbon atoms, water, about 10% to about 30% hydric solvent, preferably about 20% hydric solvent, and free acid, preferably free fatty acid, such that the pH of a 10% aqueous solution of the soap bar is no greater than about 9.
In accordance with another exemplary embodiment of the present invention, a soap bar is provided that comprises, by weight, at least about 50% soap having alkyl chain lengths of 8-10 carbon atoms. The soap bar exhibits a log reduction against Gram positive bacteria of at least 3 after 30 seconds of contact at 40xc2x0 C., as measured against S. aureus. 
In a further exemplary embodiment of the present invention, a method of making a soap bar that exhibits antibacterial effectiveness is provided. The soap bar comprises, by weight, at least about 50% soap having alkyl chain lengths of 8-10 carbon atoms, and water. The process comprises combining a neutralizing agent and fatty acids having alkyl chain lengths of 8-10 carbon atoms to form a soap solution and manipulating the composition of the soap solution, if necessary, so that a pH of a 10% aqueous solution of the soap bar is no greater than about 9. The process further includes removing a portion of water from the soap solution, optionally adding adjuvant ingredients, and solidifying to form the soap bar.
The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.
In one exemplary embodiment of the invention, the soap bars comprise at least about 45%, and preferably about 50%, by weight, of salts of monocarboxylic fatty acids having alkyl chains of 8 carbon atoms (C8), or 10 carbon atoms (C10), or a mixture of salts having alkyl chains of 8 and 10 carbon atoms. Counterions of the salts may include sodium, potassium, ammonia and alkanolammonium ions, although sodium is generally the preferred counterion.
In yet a further embodiment of the invention, the soap bars comprise less than 1.5%, preferably less than 1%, by weight, of salts of monocarboxylic fatty acids having alkyl chains of 12 (C12) to 16 (C16) carbon atoms, as Applicants have found that, as the presence of such salts increases, the antibacterial effectiveness of the soap decreases. In a more preferred embodiment of the invention, salts of monocarboxylic fatty acids having alkyl chains of 12 to 16 carbon atoms are substantially completely absent from the soap bars of the present invention. As described in more detail below, the soap bars are formed to comprise a free acid content such that a 10% aqueous solution of a soap bar of the present invention has a pH no greater than about 9.5, preferably no greater than about 9. Not wishing to be bound by any particular theory, it is believed that the soap molecules formed in accordance with embodiments of the present invention provide more free monomers in solution than longer chain soap molecules. These monomers, in a more acidic environment, may disrupt the bacteria cell membrane, resulting in rapid cell death.
In accordance with further embodiments of the present invention, the soap bars comprise compositions which assist in the formation of solutions and/or prevent or reduce formation of dispersions. For example, in such embodiments, the soap bars comprise a hydric solvent, preferably about 10% to about 30% by weight, and most preferably oil the order of about 20% by weight. The hydric solvent may comprise any now known or hereafter devised solvent, for example, an exemplary hydric solvent includes propylene glycol.
In another exemplary embodiment of the invention, the soap bars may comprise minor amounts, preferably no more than 5% by weight, of salts of monocarboxylic fatty acids having alkyl chains of 18 (C18) or more carbon atoms to provide structure in the finished soap bars and prevent or retard disintegration of the soap bar on exposure to water.
In yet another exemplary embodiment of the invention, the soap bars may be formed using water-soluble polyhydric organic solvents. Polyhydric organic solvents suitable for use in producing soap bars in accordance with the various embodiments of the present invention include, but are not limited to, propylene glycol, dipropylene glycol, butylene glycol, ethylene glycol, 1,7-heptanediol, monoethylene glycols, polyethylene glycols, polypropylene glycols of up to 8,000 molecular weight, mono-C1-4 alkyl ethers of any of the foregoing, mixtures thereof, glycerine, and any sugar alcohol, such as, for example, sorbitol.
The soap bars in accordance with the present invention may also contain other optional adjuvant ingredients that are present in sufficient amount to perform their intended function and that do not adversely affect the antibacterial efficacy of the soap bar composition. Such optional ingredients typically are present, individually, from about 0% to about 2%, by weight of the soap bar, and, collectively, from 0% to about 10%, by weight of the soap bar.
Classes of optional ingredients may include, but are not limited to, dyes, fragrances, pH adjusters, chelating agents, preservatives, stabilizers, colorants, polymers such as synthetic high polymers, derivatives of natural polymers such as modified cellulosic polymers, gums, and the like, antibacterial active agents, and similar classes of optional ingredients known the art.
A process for making the soap bars in accordance with one exemplary embodiment of the present invention will now be described. The soap components of the soap bars may be manufactured by mixing a fatty acid or acids and at least one neutralizing agent in an open agitated reaction vessel at atmospheric pressure and heating to a temperature sufficient to melt the fatty acids, generally at least about 80xc2x0 C. to 90xc2x0 C. The fatty acids include monocarboxylic fatty acids having alkyl chain lengths of 8 carbon atoms (C8) or 10 carbon atoms (C10), or a mixture of such fatty acids. Suitable neutralizing agents for manufacturing of the soap bars of the present invention include caustic solutions, for example, sodium bases such as NaOH. The neutralizing agent neutralizes the fatty acids, forming salts of the fatty acids (i.e., xe2x80x9csoapsxe2x80x9d), such as for example, sodium, potassium, ammonia or alkanolammonium salts. The neutralizing agent may be added in an amount less than the amount of the neutralizing agent required to fully neutralize the fatty acids. In one exemplary embodiment of the invention, about 95% of the required amount of neutralizing agent needed to fully neutralize the fatty acids may be added. The temperature preferably is maintained above about 80xc2x0 C. but below about 100xc2x0 C.
Additionally, a hydic solvent, such as propylene glycol, may be added to the mixture. The mixture should comprise, preferably about 10% to about 30% hydric solvent by weight, and most preferably on the order of about 20% by weight. The hydric solvent may comprise any now known or hereafter devised solvent.
Optionally at this point, the mixture may be analyzed for free acid and the pH of the mixture manipulated accordingly. For example, the mixture may be titrated with NaOH using a pH indicator and, if necessary, the composition of the mixture may be manipulated so that a 10% aqueous solution of the resulting soap bar has a pH no greater than about 9. For example, if the pH is too acidic, more neutralizing agent may be added. Alternatively, if the mixture has a pH above about 9, more free fatty acids may be added to the composition. If free fatty acids are added, it is preferable that the free fatty acids have alkyl chains of 8 to 10 carbon atoms.
At this stage of the manufacturing process, the temperature of the reaction mixture may be raised to at least about 90xc2x0 C., preferably from about 90xc2x0 C. to about 100xc2x0 C., to evaporate a desired amount of water. Alternatively, the water may be evaporated before addition of an additional neutralizing agent or free fatty acid as described above. In one embodiment of the invention, the soap bar comprises no more than 25% water. Preferably, the soap bar comprises no more than 20% water. More preferably, the soap bar comprises no more than 15% water. When a desired amount of water has been removed from the soap component, the soap component may be cooled, optional ingredients may be added to the soap component using conventional methods, and the resulting composition may be formed into soap bars, either by pouring the composition, in a molten state, into molds, or, alternatively, by forming soap bars using conventional amalgamation, milling, plodding and/or stamping procedures as is well known in the art.
In another exemplary embodiment of a process for manufacturing the soap bars in accordance with the present invention, the soap bars may be made with a solvent. In this embodiment, the above-described process may be used, except that a polyhydric solvent is initially added to the reaction vessel and heated to a temperature of about 70xc2x0 C. to 80xc2x0 C. The neutralizing agent is then added to the solvent before the addition of the fatty acids(s) to prevent formation of gels or lumps, which would increase manufacturing time. As described above, the neutralizing agent is added in an amount less than the amount of the neutralizing agent required to fully neutralize the later-added fatty acids. In one exemplary embodiment of the invention, about 95% of the required amount of neutralizing agent needed to fully neutralize the fatty acids is added. The fatty acids are then added to the mixture while the temperature is maintained above about 80xc2x0 C. but below about 100xc2x0 C. The process may then continue as described above with the optional analyzing step, optional water removal step, the addition of optional ingredients and the formation of the soap bars.
To evidence the antibacterial effectiveness of various formulations of the soap bars formed in accordance with the present invention, time kill suspension tests were conducted, whereby the survival of challenged organisms exposed to an antibacterial test formulation is determined as a function of time. In general, the time kill method is well known in the antibacterial products industry. In this test method, a diluted aliquot of the formulation is brought into contact with a known population of test bacteria for a specified time period at a specified temperature. The test composition is neutralized at the end of the time period, which arrests the antibacterial activity of the composition. The percent or, alternatively, log reduction from the original bacteria population is calculated. All testing is generally performed in triplicate, the results are combined, and the average log reduction is reported. The choice of contact time period is at the discretion of the investigator. Any contact time period can be chosen. Typical contact times range from 15 seconds to 5 minutes, with 30 seconds and 1 minute being typical contact times.
The bacterial suspension, or test inoculum, is prepared by growing a bacterial culture on any appropriate solid media (e.g., agar). The bacterial population then is washed from the agar with sterile physiological saline and the population of the bacterial suspension is adjusted to about 108 colony-forming units per ml (cfu/ml). The table below lists the test bacterial cultures used in the following tests and includes the name of the bacteria, the ATCC (American Type Culture Collection) identification number, and the abbreviation for the name of the organism used hereafter.
S. aureus is a Gram positive bacteria, whereas E. coli is a Gram negative bacteria.